Fiber lasers are used for laser cutting, welding, and folding of metals and polymers. High peak power and nanosecond pulses enable effective marking and engraving. The additional power and better beam quality provide cleaner cut edges and faster cutting speeds. A fiber laser typically comprises an oscillator and multiple stages of fiber amplifiers. The oscillator sets the laser's wavelength, pulse width, and repetition rate, while the fiber amplifiers boost the laser power to a required level.
Currently a fiber amplifier system used in a fiber laser comprises multiple amplifier stages working in tandem. Each amplifier stage increases the laser power by a limited factor—typically, a factor between a few to a few tens. For example, a fiber amplifier system 100 is shown in FIG. 1 comprising an amplifier 102 (first amplifier stage), an amplifier 104 (second amplifier stage), and an amplifier 106 (third amplifier stage). Pump laser diodes 108, 110, and 112 are coupled to amplifiers 102, 104, and 106, respectively. Optical directional isolators 114, 116, and 118 are coupled to the outputs of amplifiers 102, 104, and 106, respectively. A laser beam from an oscillator enters first amplifier 102, is amplified in amplifiers 102, 104, and 106, and finally leaves third amplifier 106.
Each amplification stage also requires a printed circuit board (PCB) for controlling pump laser diode, a laser cooling mechanism, a pump light transfer fiber optic patch cord, and a pump coupling wavelength-division multiplexer (WDM) (all not shown). The cost increases as the number of required amplifier stage increases. Furthermore, the tandem fiber amplifier scheme has very long fiber path and has many fiber junctions between amplifiers. The long fiber path and large number of fiber junctions impose reliability issue for the fiber laser. Accordingly, better performance and lower cost fiber amplifiers for fiber lasers are desired.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention.